Sound amplifier



' Sept. 8, 1925. 1,552,631

A. K. MILLER SOUND AMPLIFIER Filed March 1'7. 1923 Patented Sept. 8, 1925.

UNITED STATES PATENT OFFICE.

SOUND AMPLIFIER.

Application filed March 17, 1923.

To all whom it may concern:

Be it known that I, ALFRED K. MILLER, a citizen of the United States, residing in Santa Monica, county of Los Angeles, Stat of California, have invented new and useful Improvements in Sound Amplifiers of which the following is a specification.

This invent-ion relates generally to sound amplifiers or amplifying horns; and although my invention is not limited to phonographic apparatus or the like I illustrate and describe it here as applied to phonograph mechanisms. It Will be understood that the amplifier may be used in any situ ation wherein it is desired to amplify sounds.

It is one of the objects of the present invention to provide an amplifier not only of great amplifying efficiency as applied to any particular sound, but also one that has a large range of resonance and amplifying action. Amplifiers of which I am aware are characterized by low general amplifying eiiiciency and also by having .very low range of amplifying resonanceQ In other words, the present amplifiers are characterized by having a comparatively limited sound range in which they resonate eifioiently; and this results in certain soundssounds of certain pitches or certain tone qualities-being amplified far .more than other sounds. A very good instance of this is the case of an amplifier in connection with the phonograph or a radio instrument, where the blaring out of certain sounds is very noticeable. It is an object of my invention to produce an amplifier that obviates these shortcomings and gives a uniform high resonanceand amplification throughout the range of sounds that a phonograph, radio instrument, etc., produce.

I have found that I can attain my objects by constructing an amplifier-21. horn-the walls of which are under a permanent stress or tension; and alsoby associating with such a horn a series of stressed resonantly vibratory members collectively having a large range of resonance. A typical and specific form of such a horn, illustrative of my invention, is explained in detail in the following specification, reference for this purpose being bad to the accampanying drawis called upoirto re- Serial No. 625,776.

Fig. 1 is a vertical section of a phonograph instrument equipped with my improved amplifier;

Fig. 2 is a plan and horizontal section of the amplifier;

Fig. 3 is a fragmentary enlargement of a portion of Fig. 2;

l iig.- at is a section on line 4r-f of Fig. 8; am

Fig. 5 is a section taken as indicated by line 55 on Fig. 2, but illustrating the mode of assembly of the horn walls.

In the drawings I show. atlO a phonograph case and my improved amplifier is shown in the usual position in this case, being suspended from the motor board 11 by the flange 12 at theupper and smaller end of the horn. I prefer to mount the horn exclusively by this flange at its smaller end, leaving the large end of the horn free from contact with the case; as is illustrated in the drawings where I show the case opening 13 large enough to clearthe large end of the horn. i

The greater part of the length of the horn is a slightly tapering curved tube, preferably in this particular case of square crosssection; and at the forward or larger end of this tube the horn flares more abruptly. This forward flaring end of the horn may have its walls made integrally with the walls of the horn tube, and. the tension and other characteristics and qualities that I hereinafter describe as applied to the walls of the horn may apply to the flared forward por tion of the horn; or the forward portion of the horn may be constructed independently of the tube portion and afterwards joined to it. I prefer the first mentioned arrangement, so that the walls of the flaring portion of the horn are under tension in the same manner as I describe more particularly for the tube portion of the horn.

The horn in general has an-upper wall 15 that has a substantially even curvature throughout the extent of the tube portion of the horn and then curves-more abruptly upward at 16 and then, in a reverse curve, curves forwardly at 17 to theupper edge of the outer larger end of the horn. The lower hornwall 18 has a substantially uniform curvature throughout the tube portion of the horn and then extends on forward substantially in that same curvature so that it extends at the point 19, somewhat upwardly; and then curving reversely it curves downwardly at to the forward larger end of the horn. The t wo side walls 21 may be substantially flat asviewed in plan as in Fi 2 throughout the length of the tube portion; and then they curve outwardly as at 22 and then, curving reversely but still outwardly; as at 23 they reach the forward larger end of the horn.

These Walls are preferably made of some material that will take and keep a permanent stress. A rather hard elastic metal is a good illustration of such a material. And I may here say that I Find that a metal horn constructed in accordance with my invention does not have the undesirable qualities that are usually inherent in a metal horn. My horn does not have what is ordinarily recognized as a metallic resonance.

I find that materials that will not take and keep a permanent stress or tension will not produce the results I attain with my amplifier. For instance, such materials as fiber, bakelite, wood, unless of some special kind that I have not tried, will not keep a permanent tension but will ultimately set in the curvatures of the horn walls and will lose the tension that is orginally applied to them. And when they lose this tension the horn loses its effective resonating and an1plifying qualities.

In order to put the upper and side walls 15 and 21 under tension I form those walls integrally by first either resiliently bending or permanently founing the upper wall 15 to its proper curvature and formii side walls 21 in such relation to upper w. 15 as is shown in 2 and 5. I then have an upper and side wall structure with the upper'wall in the curved formation shown in Fig. 1 and with the side walls flaring out wardly toward their lower edges shown. in Fig. 5. It will be recognized that the side walls may be initially formed of the same piece of material as the top wall or they may be formed of separate pieces and attached to the top wall as my brazing. Then the side walls are put under tension by drawing them inwardly and attaching their lower edges to the edges of bottom wall 18. as by brazing. This also puts top wall 15 under tension even if the top wall has been initially permanently set in the curvature shown in Fig. 1.

The lower wall 18 is put under tension by being bent resiliently, without being permanently set, into the curvature shown in Fig. 1. Thus, when the four walls are assembled, each of them is under a permanent tension; and this preferably may apply as well to the flaring larger end of the horn as to the tube portion.

Mounted upon one wall of the horn, preferably lower Wall 18, are two series of res onating tongues 25 of graduated lengths, the shorter ones at the smaller end of the tube portion and the larger ones near the larger end of the horn. These series of tongues may extend, as illustrated, throughout the length of the tube portion; and they are preferably formed integrally with bot tom wall 18. The sheet of material of which the bottom wall is made is turned up and inwardly at its edges as illustrated at 26; and the upstanding tongues are formed by slitting the tip-turned edge material; and the inset at puts these tongues in a posh tion where they .do not touch side walls 2i. Each tongue 25 is then twisted as indicated in the dra vings; and this twisting enables their edges to over-lap and pass each other without touching when bottom wall 18 is bent to proper curvature; and this twisting and also the insetting at 26 has the effect of putting each tongue under a tension (stiffening each tongue). The bendin of bottom wall 18, after the tongues are formed, also has the effect of putting the metal of each tongue under a permanent tension.

The tongues 25 in the device here illustrated are formed of such various lengths as to make them, collectively, resonantly responsive to the whole range of tones emitted from a phonograph. As an instance of a design that will accomplish this resonance, I may say that the drawings show the rjlevice in substantially correct proportion; the metal of which the tongues and walls are formed being a hard sheet bronze about one thirty-second of an inch in thickness. l tind that this construction and ]')ro ')(u'li(m gives very good results in combination with the horn walls constructed hcreinbefore described. The tongues are resonantly responsive to a wide range of sounds; and the horn walls being, as they are. under tension. present relatively hard surfaces to the sound waves, and therefore the wall surfaces do not either vibrate loosely or vibrate in any pe culiaror accentuated character and therefore do not accentuate any kind of sounds extent at the expense of others.

The forward or larger curl of the horn is here shown similar to the :unplilier hat forms the subject matter of my, (yoapplication Serial No. 15 1-534, filed March 22, 1921. and entitled Sound ai'i'iplitier.

It will be noted that, in twisting tongues 25 to make them pass each other and to put them under tension, I prefer to twist them to diagonal the positions shown in Figs. and 3 rather than to the opposite diagonal positions. That is, I prefer to have them, as viewed in plan converge toward the forward end of the horn and so that the rear edge of one tongue lies outside the forward edge of the next tongue toward the rear end of the horn. This specific arrangement is the better of the two as it tends to lilll constantly direct and reflect the sound waves back into the center of the horn rather than allow them to be entrapped between the tongues and side walls 21.

Having described a preferred form of my invention, I claim a 1. A sound amplifier embodying a hollow structure expanding in size toward one end, its walls being formed of elastic material, its top and bottom walls being curved and at least one of them being elastically bent to curvature, and its side walls being con nected with the other curved wall at its edges and the side walls and last mentioned curved wall being under stress caused by bringing the side walls inwardly toward each other to connect with the first mentioned curved wall, substantially as described.

2. A. sound amplifier embodying a hollow structure expanding in size toward one end, and a series of transverse resonant tongues of graduated sizes within the structure formed integrally with one wall of the structure and extending along and standing close spaced to an adjacent wall.

3. A sound amplifier embodying a hollow structure expanding in size toward one end, and a series of transverse resonant tongues of graduated sizes within the structure formed integrally with one wall of the structure and standing substantially perpendicular to that wall near but inset from its edges.

4. A sound amplifier embodying a hollow structure expanding in size toward one end, having two opposite curved walls, and side walls joining the edges of the two curved walls, and a series of transverse resonant tongues of graduated sizes connected at their bases with a curved wall and standing close spaced to a side wall, the concave wall and tongues being formed of a hard elastic material and being under permanent stress induced by elastically bending the concave wall to form.

5. A sound amplifier embodying a hollow structure with a plurality of walls, and a series of vibrating tongues fixed at their bases to one wall near its edge, the series extending along that edge and along and close to the adjacent wall, the longitudinal extent of each tongue being substantially parallel to said adjacent wall.

6. A sound amplifier embodying a hollow structure with plurality of walls, and a series of vibrating tongues fixed at their bases to one wall near its edge, the series extending along that edge and along and close to the adjacent wall, the longitudinal extent of each tongue being substantially parallel to said adjacent wall, and the transverse extent of each tongue lying at a slight angle to the line of the series of tongues.

7. A sound amplifier embodying a hollow structure with walls, and a series of vibrating tongues fixed at their bases to one wall, the series extending longitudinally of the structure, and each tongue standing in a plane somewhat at an angle to the line of the series of tongues.

In witness that I claim the foregoing I have hereunto subscribed my name this 9th day of March, 1923.

ALFRED K. MILLER. 

